1. Field of the Invention
The present invention relates to a method for preparation of membranes of metal/ceramic composite materials, particularly tubular membranes having high plating uniformity on a production scale.
2. Discussion of the Background
The procedure for electroless plating of palladium on substrates is well developed and involves several steps where the substrate is contacted with various solutions in a certain sequence. The existing technology is based upon immersing appropriate substrates in the plating bath solutions covering areas of the substrate by Teflon tape where plating is not desired. This technique has been used for preparing composite membrane disks [Ilias et al, Separation Science and Technology, 32(1-4), pp 487-504, 1997] as well as tubular membranes [Collines and Way, Ind. Eng. Chem. Res., 32 pp 3006-3013, 1993]. In case of disk membranes, one side of the membrane as well as the cylindrical side area is covered by Teflon tape to allow plating on one surface of the disk. In the case of tubular membrane the exterior surface of the tube is covered by tape to allow plating on the inside area of the tube.
The existing technology for electroless plating of palladium is manual and would be difficult to scale up to long commercially available tubular substrates which are typically up to 1 m in length. The plating in such long tubes by the prior art of immersing substrates in solutions is also not likely to be uniform. This technique is only adequate in preparing small samples as described in the above referenced publications. However, a technique amenable to mechanization is needed to prepare large scale membranes for practical applications.
Thin films of palladium allow pure hydrogen (H2) to pass through from a gas stream. Separation and purification of H2 is becoming a focus of many RandD efforts around the world, as energy and environmental issues continue to be at the economic and political forefront.
The thin films of Pd used for H2 separation are typically formed inside of tubular substrates. Past methods for depositing thin films of Pd used electroless plating. This process was never considered ideal, and long tubes (more than 12xe2x80x3) were difficult to achieve. The H2 purity would inevitably suffer in the longer tubes because the uniformity of the film thickness could not be controlled.
Accordingly, one object of the present invention is to provide a method for the preparation of metal/ceramic composite membranes that allows for large scale production with high uniformity in the thin metal layer.
A further object of the present invention is to provide a method for hydrogen separation using the metal/ceramic composite membranes that provides high purity hydrogen production on a large scale.
These and other objects of the present invention have been satisfied by the discovery of a method for producing a metal plated ceramic surface, comprising:
flowing an electroless plating bath solution of metal to be plated over a first surface of a porous substrate, and
concurrently applying a pressure of gas on a second surface of the porous substrate opposite to said first surface, such that said ceramic substrate separates the solution of metal from the gas.